The Spread of Sinus Activation During Potassium Administration

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Abstract
Electrodes were chronically implanted in intact dogs at several locations on the atria and ventricles, and studies made of the effect of an elevated extracellular K+ concentration on the spread of the sinus impulse throughout the atria. It was found that sinus activity propagates to the coronary sinus and ventricles at a time when the atrial muscle fibers have been rendered inexcitable. The finding of such a sino-ventricular rhythm supports the existence of a specialized conducting path between the sinus and the atrio-ventricular node; this path is particularly resistant to depolarization by potassium. Potassium-induced 2:1 sino-atrial block was described. In vitro experiments provided a demonstration that such block is frequency-dependent and due to marked prolongation of the refractory period provoked by high [K]0. It appears that the lengthened refractory period may be due to a marked reduction of the reactivation rate of the "sodium carrying system."

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